In order to provide a smaller-sized semi-conductor device package, new package structures such as Ball Grid Array Package (BGA) structure and Chip Scale Package (CSP) have been proposed and employed practically. As an electro-conductive sealing element of the semi-conductor package, a composite element composed of an aromatic polyimide film and a metal film placed on the polyimide film is employed. The aromatic polyimide film should have a high dimensional stability and a low water absorption and accordingly the polyimide film is typically made of polyimide comprising a 3,3′,4,4′-biphenyltetracarboxylic acid unit and a p-phenylenediamine unit.
For the manufacture of a semi-conductor device package, a semi-conductor device is connected to a circuit board of electro-conductive sealing element and sealed with resinous material. In the course of manufacture of a semi-conductor device package, moisture vapor is produced within the semi-conductor device package, and the moisture vapor has to be removed from the device package.
The aromatic polyimide film of polyimide comprising a 3,3′,4,4′-biphenyltetracarboxylic acid unit and a p-phenylenediamine unit shows a small moisture vapor-transmission ratio. Accordingly, it takes a considerably long period of time for removing the moisture vapor produced in the semi-conductor device package through the sealing element.
In order to shorten the period of time required for removing the moisture vapor from the package, it has been proposed to employ an aromatic polyimide film prepared from pyromellitic dianhydride and a diamine compound. This pyromellitic acid-type polyimide film shows a relatively high moisture vapor transmission ratio, but shows a low tensile modulus. Accordingly, the aromatic polyimide film of the electro-conductive sealing element should have an increased thickness to impart enough tensile strength to the sealing element. The increased thickness of the polyimide film is disadvantageous for manufacturing a circuit board having an increased fine circuit pattern.
For preparing the electro-conductive sealing element, a copper film is placed on the polyimide film. The copper film is generally combined to the polyimide film using adhesive. However, the use of adhesive results in increase of thickness of the sealing element. The increased thickness of the sealing element is disadvantageous for manufacturing a small-sized semiconductor device package.
A sealing element in which a copper film is directly plated or deposited on the aromatic polyimide film has been already proposed and employed. Since a surface of the conventional aromatic polyimide film shows low adhesiveness, it has been proposed to apply a surface-activating treatment to the polyimide film. Examples of the surface-activating treatments include wet processes such as desmear treatment and alkaline treatment and dry processes such as atmospheric pressure plasma discharge treatment and corona discharge treatment. The wet process is disadvantageous in that sufficient washing is required. The conventional dry process cannot impart satisfactory adhesiveness to the aromatic polyimide film.
Accordingly, it is an object of the present invention to provide an electro-conductive sealing element for manufacturing a packaged semi-conductor device which requires a shortened drying period of time and particularly to provide an electro-conductive sealing element composed of an aromatic polyimide layer and a copper layer having such advantageous features.